1. Field of the Invention
The present invention relates to an apparatus for filling insulation material into a super low-temperature storage tank and to a method thereof. More particularly, the invention enables to fill insulation material between internal and external walls of a storage tank by radio remote and/or wire control and easily monitor the states of filling, thereby maximizing the efficiency of system management and moreover facilitating of an easy operation of the apparatus.
2. Description of the Related Art
In general, along with the development of petroleum chemistry industry and natural gas industry, the use of liquefied petroleum gas (LPG) and liquefied natural gas (LNG) has been drastically increased and accordingly the need to construct a super low-temperature storage tank for storing those gases is growing.
In order to transport or store large amounts of those LPG and LNG, because it is very difficult to transport them in the state of gas, there has been used a method of liquefying those gases at a super low temperature and a high pressure. The method allows an easy storage and transportation of those gases at a low cost in large scale.
However, the super low-temperature storage tank needs to be kept in hundreds degrees below zero and thus is exposed to breakage due to the cold shortness of metal. Besides, as the contents are potentially dangerous gas compressed at a high pressure, its manufacture needs a high technique.
The super low-temperature storage tank needs vaporization control and heat intake control, for the liquid stored is vaporized by intake of outer heat. Normally the ratio of vaporization is restricted to 0.05 to 0.2 %/day. In order to satisfy the ratio of vaporization, the maximum permissible heat-intake should be under control and a proper insulation system is demanded.
Moreover, even in the system specifically designed to operate at a certain temperature by using an insulation system to thereby prevent from the loss of vaporization, if there is a difference of temperature from outside, the heat stream is facilitated and causes problems. Therefore, to block such heat stream, an appropriate insulation material is filled in about 0.5 m to 1 m of insulating space between the internal and external walls of the tank, thereby reducing the vaporization of the gas stored.
As for the insulation materials, an expansion perlite has been used mostly. The insulation material is supplied to the vacant space between internal and external walls of the storage tank through a multiple number of nozzles formed on the roof of the tank. The insulation material supplied mainly blocks out the heat from outside and keeps the gas inside safely at a super low temperature. However, the insulation material supplied to the storage tank consists of minute particles of irregular forms and there should be an unnecessary space among particles, thus unless a very effective filling is conducted, which results in the decrease of filling efficiency of the insulation material and finally reducing the performance of insulation.
Furthermore, while the insulation material supplied is sinking, dews are formed on the external wall and dried. Occasionally, even frosts formed result in the increase of vaporization, which may extend the operational time of the compressor in the liquefaction facility. In the extreme case, the compressor cannot stand the overload, causing a fire or more serious problem of discharging surplus gas.
In order to solve such problems, when filling insulation material between the internal and external walls of the low-temperature storage tank, a vibrator is used for compulsively vibrating the material filled, thus leading to the more efficient filling.
If the compulsory vibrating step is missed out of the filling process, the insulation material filled in LNG storage tank is naturally sinking after a certain period of time. The sinking of the insulation material is led to a vacation of the upper space of the tank, causing the formation of ice on the wall of the tank. Besides, while operating, the tank is contracted and thus in need of replenishment of the insulation material. Consequently the tank is exposed to a danger of an inflammation or an explosion of the gas, or even the toxicity of the gas, which may lead to a potential loss of lives.
Therefore, the most effective and compulsory way to fill insulation material, to enhance the performance of insulation and to safely maintain the liquid stored is to perform the step of filling the insulation material simultaneously with compulsively vibrating the tank by using the vibrator.
As for the design where the external wall of the storage tank is formed of metal, there have been proposed U.S. Pat. Nos. 4,633,086, 4,614,436 and 3,633,878 wherein a magnetic vibrator is attached to the metal wall so that the vibrator vibrates the metal wall, thus inducing the insulation material filled in compact through the compulsive vibration.
However, the method of inducing the vibration from the vibrator to the insulation material for the compressed filling is problematic in that the insulation material cannot be filled evenly all over the area. Moreover, as the vibrator is magnetically attached to the external wall, the method is not applicable to the structures where the external wall is made of concrete or the insulation material is attached between internal and external walls.
On the other hand, the method where the insulation material is filled into the super low-temperature storage tank whose external wall is made of concrete has been proposed in U.S. Pat. No. 3,731,907 and Europe Patent No. 39785A1. However, with the structure, the ratio of filling cannot be expected and thus the worker has to measure the ratio by using a manual tool such as a thread or a tapeline inside the storage tank, which is very dangerous for the worker. On top of it, while vibrating, the worker needs to check the state of vibration inside the tank by hand every moment and is always exposed to dusts swirling inside the tank, which is bad for the worker""s health.
In a conventional technique, a vibrator is directly sunk in the insulation material, thereby enabling of a compressed filling. It, however, is also difficult to measure the accurate rate of the sinking and even needs re-filling work and therefore it not only requires lots of effort and costs but also takes long period of time to finish. Specifically, It is very risky job for the worker to enter the tank and check by hand the rate of sinking inside the tank.
Accordingly, in order to solve the aforementioned problems, it is an object of the present invention to provide an apparatus for filling insulation material between the internal and external walls of the storage tank by radio remote and/or wire control while accurately monitoring the state of filling, thus maximizing the efficiency of the system operation.
Another object of the present invention is to provide a method of filling insulation material by radio remote and/or wire central-control from outside the tank and thereby enhancing the convenience of the work as well as ensuring safety by removing any potential dangerous factors.
In order to accomplish the aforementioned objects, the apparatus for filling insulation material comprises: a vibration means made up of a vibration plate element vibrating buried in the insulation material supplied between the internal and external walls of a super low-temperature storage tank, a lower plate connected to attach and detach the upper part of a shaft of the vibrating plate element, a vibrator for generating the vibration installed on the lower plate and furthermore vibrating the vibrating plate element via the lower plate, and an upper plate for covering the vibrator, connected to the lower plate through a plurality of vibration buffering elements and having a rolling element to enable of rotation by a plurality of support shafts; a lift driving means made up of a winding motor, a drum revolving by the winding motor, and a wire wound up on the drum wherein the lower part of the wire is wound up on the rolling element of the vibrating means so as to drive the vibrating means along with the ratio of winding the wire; a horizontal transporting means wherein a pair of rollers are installed to transport by a transport motor without digression in slide along a guide rail attached on a bracket on a ceiling of the storage tank and rolling at a certain intervals supported by the first, second and third support frames, the first to third support frames working continuously with a connection frame; an automatic winding means interlocked to the second support frame of the horizontal transporting means at one side of the lift driving means, one end of its cable being wound up on a winding roll and the other end of its cable being connected to the vibrating means; a level sensing means connected to the third support frame of the horizontal transporting means on the other side of the lift driving means and controlling the filling amount of the insulation material filled in a spacious part between the internal and external walls of the storage tank; a flux preventing means made up of a bracket attached to the lower and upper plates of the vibrating means to project out and upwardly and a tamping roller shaft-supported to revolve on an end part of the bracket and buffering the collision impact between the internal and external walls of the storage tank as well as maintaining in stability the horizontal flux and verticality of the vibrating means; a descending position sensing means placed lower than the vibrator on both sides of the vibrating means and restricting the descending position of the vibrating means by touching the insulating material; a controlling means for checking the filling amount of the insulation material filled by a signal received from the level sensing means and thereby remote-controlling the driving means, the horizontal transporting means and the vibrator; and a display means made up with a camera integrated with the vibrating means, a lighting lamp and a monitor capable of a direct observation of the inside through the camera from outside of the storage tank.
Furthermore, the present invention provides a method of filling insulation material comprising the steps of: filling the insulation material at a certain height between the internal and external walls of a storage tank; lowering a vibrating means by driving a lift driving means; stopping the descending of the vibrating means automatically at the same when a descending position sensing means connected to the vibrating means comes in contact with the insulation material filled; driving a vibrator of the vibrating means to vibrate a vibrating plate element inserted into the insulation material, thereby compressing the insulation material filled; stopping the driving after the vibrating means is operated for a predestined time; elevating the vibrating means by driving the lift driving means; transporting the structure connected to a horizontal transporting means by a certain pitch along a guide rail by driving the transporting motor of the horizontal transporting means; checking the levels of the filling of the insulation material by using a level sensing means at a random transporting position of the horizontal transporting means; and repeating the step of lowering the vibrating means by driving the lift driving means at the aforementioned position.